1. Field of the Invention
This invention relates to manufacturing a hollow plastic product having at least one unitary, substantially solid attachment projection extending outwardly from an exterior surface. More specifically, this invention relates to a method for manufacturing a hollow plastic product using combined blow molding and squeeze molding techniques.
2. Description of the Prior Art
The manufacture of hollow plastic products using blow molding techniques is well known to those skilled in the art. Exemplary of such products are motor vehicle fuel tanks blow molded of polyethylene or other suitable homopolymer, copolymer or polymer alloy materials. It frequently is necessary or desirable to attach devices to such hollow blow molded products without disrupting the integrity or continuity of the plastic wall of the product. It is frequently desirable, for example, to attach a heat shield or other device to the exterior surface of a blow molded plastic fuel tank for a motor vehicle. Various attachment techniques are known for this purpose. Thus, for example, a suitably sized and configured plastic attachment piece can be welded to the exterior surface of the tank. The separate welding operation subsequent to the blow molding of the hollow plastic product, however, involves increased costs and complexity. The same is true of various other known methods of providing an attachment piece, such as adhesive attachment thereof to the exterior surface of the hollow plastic product. Accordingly, an improved method is needed for providing such attachment sites.
It is accordingly an object of the present invention to provide an attachment site on the exterior surface of a blow molded hollow plastic product. It is a particular object of certain preferred embodiments of the invention to provide such attachment site without the cost and complexity of a separate manufacturing operation, i.e., a manufacturing operation subsequent to the blow molding operation, for securing an attachment piece to the exterior surface of the product.
One method and apparatus for manufacturing a hollow plastic product is taught in U.S. Pat. No. 4,659,531 issued Apr. 21, 1987 to Ezaki. According to that teaching a mold half is provided having a tubular groove portion corresponding to the exterior surface of the desired hollow plastic product. The mold half also has an additional contour, specifically, a projecting groove section which extends outwardly from the tubular groove section. It is taught to supply a molten plastic parison into the tubular groove portion and separately a clump of molding material into the projecting groove section. According to Ezaki, when blow molding is carried out by introducing a pressurized gas into the parison, the aforesaid clump of molding material becomes integrated with the parison, thereby providing a hollow plastic product of unitary structure. Although Ezaki asserts that it is an advance over the previously known methods for manufacture of a hollow plastic product having a projection outwardly from the exterior surface of a main body, it nevertheless is disadvantageous in that it calls for the separate steps of providing a parison and providing a clump of molding material into the molding tool. As will be understood from the disclosure below, the present invention represents a significant advance in the art and, specifically, is an advance over the teachings of Ezaki.